diff --git a/krebs/3modules/exim-smarthost.nix b/krebs/3modules/exim-smarthost.nix
index 7b3dace6a..093ae2030 100644
--- a/krebs/3modules/exim-smarthost.nix
+++ b/krebs/3modules/exim-smarthost.nix
@@ -40,7 +40,7 @@ let
     };
 
     extraRouters = mkOption {
-      type = types.nullOr types.str;
+      type = types.nullOr types.lines;
       default = null;
     };